1. Field of the Invention
The present invention relates to an image stabilizer for correcting image blurring arising from camera shake in cameras and other optical apparatuses.
2. Description of the Related Art
A mechanism for shifting some lenses of a lens unit constituting an imaging lens in perpendicular to the optical axis of the imaging lens is incorporated in a vibration-proof optical system for controlling image blurring in a camera. Image blurring is predicted by detecting acceleration of the camera resulting from camera shake and the imaging lens is shifted in perpendicular to the optical axis of the lens in response to the prediction.
In such a lens shifting mechanism, as disclosed in Japanese Patent Laid-Open No. 3-188430, camera shake is resolved into a component in the horizontal direction of the camera (hereinafter referred to as yaw direction) and a component in the vertical direction of the camera (hereinafter referred to as pitch direction), and an image-blurring correction shift lens (hereinafter simply referred to as a correction lens) slides in both the yaw direction and pitch directions with the aid of a guide bar and bearings or with the aide of slide plates mutually sliding to each other so that the correction lens is shifted in the yaw direction and the pitch direction mutually independently without any displacement in the direction of the optical axis.
Japanese Patent Laid-Open No. 63-155038 discloses a mechanism in which a correction lens is supported by a four-joint parallel link with its rotation about the optical axis restrained. The movement of the four-joint parallel link in the optical axis direction is absorbed by a guide and a spring so that the movement of the link does not affect the correction lens, and the correction lens is urged against a reference surface by the spring with the aid of a ball.
Japanese Patent Laid-Open No. 5-297443 discloses a mechanism in which, besides a member that restrains the rotation of a correction lens about the optical axis, at least three supports such as balls are provided between a support frame and the correction lens. Pressure means is used to urge the correction lens. The correction lens is shifted so that it keeps reliably its upright position to the optical axis.
Japanese Patent Laid-Open No. 7-294975 discloses a mechanism in which a correction lens is moved back and forth independently in an X axis (yaw) and a Y axis (pitch) by feed screws. In this mechanism, a roller is arranged between a correction lens frame and a movable member so that the correction lens is shifted in all directions. A ball under the urging of a spring is arranged between the correction lens frame and a base so that the correction lens may not be inclined.
Besides these disclosures, it is contemplated that a correction lens is put back to its initial position by the balance of a plurality of spring members with the restoring force of each spring member (helical tension spring) used as means for restraining the rotation of the correction lens about its optical axis.
The above-cited Japanese Patent Laid-Open No. 3-188430 has two disadvantages: one is that a great frictional resistance in sliding the sliding plates requires large energy that is used to generate electromagnetic force required for shifting the correction lens and the other is that, strictly speaking, a slight looseness in the engagement of the guide bar and the bearing causes the correction lens to be displaced in the direction of the optical axis.
In the above-cited Japanese Patent Laid-Open No. 63-155038, a looseness takes place between the optical axis and the vertical direction of the mechanism because a lens barrel and a ring member are loosely engaged with each other. During the driving of the mechanism, a frictional resistance takes place in the engagement portion, canceling the merit of the hinge portion of the link having a small frictional resistance and the ball having also a small frictional resistance. The use of the coordinated support of the four-joint parallel link and ball makes the mechanism complex, increases the component count of the mechanism, and pushes up the cost of the mechanism. In this disclosure, the shift mechanism in one direction only is proposed. Even if the same mechanism is additionally arranged for the vertical direction as well, a shifting of the lens in a slant direction is difficult to perform because of the structure of the four-joint parallel link.
In the above-cited Japanese Patent Laid-Open No. 5-297443, the means for restraining the rotation of the correction lens about the optical axis is the sliding motion acting between the guide bar and the bearing and between an elongated slot and a pin. Frictional resistance here is not small enough. Besides the means for restraining the rotation of the correction lens about the optical axis, at least three balls and the pressure means are employed, making the mechanism complex, increasing the component count of the mechanism, and pushing the cost of the mechanism.
In the above-cited Japanese Patent Laid-Open No. 7-294975, a frictional resistance is generated between the guide of the movable member and a guide shaft, and the roller between the correction lens frame and the movable member generates rolling friction resistance, and the overall resistance generated against shifting the correction lens is thus substantial. The addition of the support mechanism of the ball makes the mechanism complex, increases its component count and pushes up its cost.
In the mechanism which employs the restoring force of the spring member (helical tension spring) and the. balance of the plurality of springs, an electromagnetic force driving unit shoulders the load of the spring members during the driving of the correction lens. The more the shift of the correction lens the greater the load shouldered by the driving unit. To precisely position control the shifting of the correction lens, the electromagnetic force driving unit must output a larger force. For this reason, the driving unit is bulky in size and needs more energy.